Using the Tesla 2170 batteries, you would need 3000 batteries for 60 KWH. That number of batteries would fit in the gen 1 battery case without problems arranged as 24 modules with 2 sets of terminals each to replicate the 48 modules in the original battery. The battery would gain a couple of hundred pounds in weight but wouldn't be any larger in volume. Since Tesla is actually a battery company, at some point Tesla is going to sell their batteries to any OEM who can order enough at one time meet their minimum. At $100/KWH that's about $6000 for the batteries alone but probably less than $10K for a rebuilt 60KWH battery. If you could fool the BMS into thinking that it is still looking at Nissan modules it could be substantially less. Panasonic is also building 2170 batteries but they don't have as high an energy density and they aren't set up on the gigafactory model.